Terbium-activated cerium magnesium aluminate phosphors are fluorescent lamp phosphors used in photocopy applications. Such a phosphor has the general formulation (Ce,Tb)MgAl.sub.11 O.sub.19 and is described in U.S. Pat. No. 4,840,747 to Fan et al., the disclosure of which is incorporated by reference.
We have found that the maintenance of a lamp containing a terbium-activated cerium magnesium aluminate phosphor can be improved, without adverse effect on the stir-in characteristics of this phosphor, if the phosphor is combined with small particle size aluminum oxide and then wet-milled, prior to its application to the interior of a fluorescent lamp envelope.